The invention relates generally to systems and methods for supporting telephony for an enterprise and relates more particularly to reducing the susceptibility of telephony systems to data network failures.
There are a variety of alternative approaches to supporting call sessions for telephones of an enterprise, such as a corporation. A traditional approach is to use a private branch exchange (PBX) to provide all of the call processing for telephony devices. The call processing by the PBX includes supporting call-related features, such as call forwarding and voice messaging, in addition to the required routing of incoming and outgoing calls.
Another known approach is to integrate the call processing with a data network, such as a local area network (LAN) of an enterprise. The separate components that are used to form a particular telephony-over-LAN (ToL) system will vary from implementation to implementation. Common components include gatekeepers, gateways, legacy PBXs, Internet Protocol (IP) phones and endpoints, and messaging servers.
An example of a ToL system is shown in FIG. 1. The ToL system includes a number of endpoints 10, 12 and 14, with each endpoint including a personal computer 16 and a telephone 18. The personal computers are configured to run ToL software. Thus, each computer may be equipped with a telephony application programming interface (TAPI) that allows the computer to have telephone capability. The telephones 18 may be digital phones. While the system of FIG. 1 includes linked computers and telephones, the device endpoints of a ToL system may alternatively be standalone IP phones, and/or the computers may be equipped with microphones and speakers that enable the computers to function as telephones.
The endpoints 10 transfer non time-critical data (such as electronic mail) and time-critical data (such as voice information) to each other using communication resources 20 of the data network 22, which is represented as a bus. The communication resources may include routers, switches and other conventional components. The computers 16 and telephones 18 are network endpoints that have unique addresses. For example, each of the computers may have a unique IP address that is used to uniquely identify the computer as the target endpoint for particular data and voice transfers.
In the example of FIG. 1, the data network 22 is a LAN. The system includes a gateway 24 and a gatekeeper 26. The gatekeeper maintains a database of the unique addresses for the endpoints of the network. Upon receiving a request for a data or voice transfer from an external telephony device to one of the network endpoints, such as the telephony-enabled personal computer 16 of the first workstation 10, the gatekeeper translates an endpoint alias (such as a host name or e-mail address) or translates a telephone address (such as an address in a telephone number format) to identify the network endpoint. The various functions of gatekeepers are known in the art.
The gateway is used to provide protocol conversions, when necessary. The gateway may translate call-processing signals and voice information from a packet-switched format used within the data network 22 to a circuit-switched format that is used by some external networks 28, such as the public switched telephone network (PSTN). The protocol conversion enables endpoints of the network 22 to communicate with external telephony devices, such as telephones, workstations of other enterprises, or workstations of the same enterprise (corporation) having facilities in more than one city. If the data network 22 is only connected to another data network, such as when networks are interconnected to form a wide area network (WAN), the gateway 24 may not be necessary, since protocol conversion may not be required.
The system of FIG. 1 also includes an off-network messaging system 30. The workstations 10, 12 and 14 may be configured to allow a user to automatically transfer incoming calls to the messaging system when the user is going to be unavailable or when the user wishes to remain undisturbed. Messages that are recorded by the system 30 may be retrieved by the appropriate users at a later time.
The utilization of a data network 22 to support telephony capability for various endpoints 10, 12 and 14 has a number of advantages. System upgrades are easily implemented. Often, the upgrade only requires the installation of software at the computers, with the software being downloaded and installed at the user's convenience. Moreover, sophisticated telephony features can be provided inexpensively, since the processing power of the computer may be employed.
Avoiding communication isolation is an important concern for corporations, whether the corporation employs separate data and telephony systems or integrates telephony and data communications support. U.S. Pat. No. 6,301,352 to Chung et al. describes a method and system that addresses the concern as applied to a network of computers that are not used for providing telephone conversations, but are linked to the PSTN in order to receive data from other computers or computer networks. Thus, there is a path from the PSTN to the LAN of computers. If the path to the LAN is disrupted, the computers will be able to interact with each other, but will be isolated from the PSTN. The Chung et al. patent specifically addresses the problem in which the path from a common channel signaling gateway to the LAN is disrupted. The Chung et al. system provides a second path to the LAN. The alternative signaling paths provide improved fault tolerance for connecting LANs to external networks.